Readily installed food processor cutter tool with negative blade lift

ABSTRACT

In order to overcome the unexpected dynamic lifting action of an easily installed rotary cutter tool in a food processor as the lower blade revolves at relatively high velocity through food material, such as shelled nuts in making nut butter, a downward inclination in a forward direction is provided in at least the lower blade, near its outer tip. If desired, such an inclination may be incorporated into both blades of the cutter tool. This downward inclination of the blade surface to provide a negative angle of attack (-A) relative to the direction of rotation may be accomplished in a preferred embodiment by twisting the outer blade portion into a negative angle of attack relative to the remainder of the blade or by mounting the whole blade onto the hub at a negative angle of attack. Thus, as the lower blade moves at relatively high velocity through food material, there is a continuous impact of the food material against the downwardly inclined blade surface at least near the tip region producing a downward component of thrust for holding the tool hub down firmly seated in its proper relationship upon the rotating drive shaft.

This is a continuation of application Ser. No. 747,412, filed Dec. 6,1976, now abandoned.

FIELD OF THE INVENTION

The present invention relates to apparatus for preparing food, and inparticular to multi-purpose kitchen apparatus in which a convenientlyremovable rotary food preparing tool having a plurality of thin rigidcutter blades is used for processing food material in the bottom of anupright working bowl.

BACKGROUND OF THE INVENTION

There is food processing apparatus of the type broadly set forth abovehaving a working bowl or vessel with a motor-driven shaft projectingvertically upwards through the bottom of the bowl on which variousselected rotary tools can be engaged to be driven by the shaft forperforming various food processing operations as may be desired by theuser. For further information about this type of food processingapparatus, the reader may refer to U.S. Pat. No. 3,892,365--PierreVerdun, and to my prior U.S. Pat. No. 3,985,304.

In this apparatus, there is used a removable cutter tool having aplurality of thin rigid cutter blades secured to a hollow hub andextending outwardly from the hub. When the user instals this removabletool, its hollow hub slides vertically down around the motor-drivenshaft. In order to provide a driving connection between the shaft andthis hollow hub, the shaft is provided with axially extending drivingcoupling means, such as a flat face keyway or splines, or a square, orhexagonal shape may be provided to achieve the positive drivingrelationship. The hollow hub has complementary coupling means, such asinternal lugs, keys, longitudinally extending relative to the length ofthe shaft for engaging the driving coupling means operatively associatedwith the rotatable drive shaft. One of these blades in the normaloperating position of this cutter tool is positioned near the bottom ofthe working bowl along the length of the blade with a small spacingbetween the bottom of the bowl and this blade.

In this type of food processing apparatus, the rotary cutter tool may bedriven at a speed in the range from approximately 750 revolutions perminute (R.P.M.) to 2,000 R.P.M. This rotary cutter tool may be used fordifferent kinds of food processing, for example, for cutting or mincingmeat, for cutting vegetables of all kinds, including condiments and forworking and preparing doughs and pastes. Even a relatively smallquantity of food material can be processed, if desired, because of thesmall spacing between the lower horizontal blade and the horizontalbottom of the working bowl, when the tool is in its normal operatingposition. The tool can also be used for preparing mayonnaise, or anyother similar emulsion, because the lower blade is closely spaced to thebottom, thereby providing a highly effective shearing, emulsifyingaction when the cutter tool is in its normal operating position.Moreover, when shelled peanuts, or shelled cashew nuts, or other shellednuts, are placed into the working bowl, the rotary cutter tool canprocess these nuts into peanut butter or cashew butter or other nutbutter.

However, in making such nut butter, using the prior art apparatus, ithas been my observation that the mass of partially chopped or pulverizednuts may tend to collect in the bottom of the bowl. The undesired resultis that the lower blade sometimes tends to "ride up" or climb whilemoving like a hydrofoil rapidly through the mass of pulverulent foodmaterial. The clearance between the lower revolving blade and the bowlbottom progressively increases until this blade is skimming or skippingalong over the upper surface of the food material. This is a dynamicallystable state, wherein the lower blade is seen skimming at high velocityover a substantially undisturbed bed of chopped or pulverized nuts uponwhich it is moving. Once the cutter tool has ridden up into thisdynamically stable lifted position, it will continue in that elevatedlocation until the machine is shut off and the food material is manuallypushed aside, so that the cutter can resume its normal down positionfully seated relative to the drive shaft.

This failure of such prior art apparatus to complete the processing ofshelled nuts into nut butter could unexpectedly occur any time. Myexperimental trials have shown that these unexpected conditions of theblade lift and climbing action up onto the top surface of the food massare more likely to occur when there is only a modest quantity of nuts inthe bowl bottom.

U.S. Pat. No. 3,493,022--Jean Mantelet does not state whether or not themincing machine described therein can actually be used to processshelled nuts into nut butter. This Mantelet patent was cited during theprosecution of the Verdun patent mentioned above, and it is discussedherein in case the reader might consider it to be pertinent prior art.In the Mantelet mincing machine, the coupling between the blade-carrierhub and the driving spindle is produced by means of inclined ramps orfins wrought on the lateral surface of the spindle on which are engagedwith a clearance correspondingly inclined grooves wrought in the lateralsurface of a central bore of the hub. The inclination of these fins andgrooves is selected, as specified by Mantelet, such that one rotation ofthe spindle in its normal direction of rotation tends to engage the finsin the grooves, that is to say, to draw the hub downwards. Theseinclined ramps or fins are said to provide an automatic engagement ofthe hub on the spindle as soon as the appliance is started and to ensurethat the hub cannot fly off during operation in any case. Such inclinedramps or fins require a difficult manipulation of the tool during itsinstallation or removal and thus is entirely different from the presentinvention in which the slicing blade itself dynamically produces a"negative lift" to hold the readily removable cutter tool in place onthe drive shaft.

In U.S. Pat. No. 3,612,125--Helmut Krauth, the upper exposed end of therotatable output shaft of the motor is screw threaded, and a suitablenut is threaded onto this upper end, so as to maintain the sleeve-shapedcarrier of the cutter blades in place. The use of such a fastening nutis time consuming for the user. Moreover, it tends to be unsanitarybecause food particles can lodge in the crevices between the nut and theexposed threaded end of the output shaft. Thus, this Krauth patent isentirely different from the present invention in which the slicing bladeitself dynamically produces a negative lift to hold the readilyremovable cutter tool in place on its drive shaft.

SUMMARY OF THE INVENTION

In order to overcome this unexpected dynamic lifting action of theeasily installed rotary cutter tool of the prior art, an improvement isincorporated into the rotary cutter tool. A downward inclination in aforward direction is provided in the lower blade, at least near itsouter tip. If desired, such an inclination may be incorporated into bothblades of the cutter tool. This downward inclination of the bladesurface to provide a negative angle of attack (-A) relative to thedirection of rotation may be accomplished by twisting the outer bladeportion into a negative angle of attack relative to the remainder of theblade or by mounting the whole blade onto the hub at a negative angle ofattack. Thus, as the lower blade slices at high velocity through a massof food, there is a continuous impact of the food material against thedownwardly inclined blade surface at least near the tip region of theblade producing a downward component of thrust for holding the tool hubdown firmly seated in its proper relationship upon the rotating driveshaft.

In the presently preferred modified embodiment of the present invention,as mentioned above, the tip portion of the lower blade or of both bladesis bent upwardly along a line of inflection to produce the downwardinclination of the upper surface of the blade.

It is my present theory of the operation of the improved tool that thedynamic forces involved are a function of the square of the relativevelocity between the rapidly moving blade and the food material, and soit is the outer portion of the blade which is dominant in producing thenegative lift.

The various features, aspects and advantages of this invention willbecome more fully understood from a consideration of the followingdescription of two illustrative embodiments of the invention whenconsidered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial elevational sectional view of the lower portion of aworking bowl with a prior art rotary cutter tool therein, illustratingimproper operation;

FIG. 2 is a plan view of a two-bladed rotary cutter tool embodying thepresent invention;

FIG. 3 is an elevational view of the rotary cutter tool of FIG. 2, asseen looking from the direction 3--3 in FIG. 2;

FIG. 4 is a plan view of a modified embodiment of the invention in atwo-bladed rotary cutter tool; and

FIG. 5 is an elevational view of the rotary cutter tool of FIG. 4, asseen from the direction 5--5 in FIG. 4.

DETAILED DESCRIPTION

As shown in FIG. 1, there is rotary food processing apparatus 10 of theprior art including a working bowl or vessel 12 of generally cylindricalconfiguration including a horizontal bottom 14 and an upright side wall16. This working bowl 12 may, for example, have an internal diameter ofsix inches or more, and for convenience of illustration, the top of thebowl is shown broken away. This bowl 12 is detachably mounted on a base18 by a complementary engaging means, such as a plurality of lateraltenons on the housing of the base 18 engageable in corresponding notchesin a skirt 20 which projects down below the bottom of the bowl 12, forexample, as shown in detail and described in the Verdun patent mentionedabove.

A vertical drive shaft 22 for driving a food processing tool extends upinto the bowl 12 with its axis of rotation extending along the centralaxis of the bowl. The base 18 houses an electrically energized motordrive mechanism as is known in the prior art for rotating the driveshaft 22.

A central hole is formed through the vessel bottom 14 to permit thepassage of the rotary driving shaft 22. In order to retain the foodmaterial being processed in the bowl, an upstanding annular well 24 ofrelatively great heigth is formed integrally with the bottom 14. Theheight of this annular wall 24 is determined for providing in the lowerportion of the vessel 12 a volume sufficient for containing the preparedfood which may include juices, milk, vegetable oils, or other liquids,as processed in the apparatus 10.

This food processor apparatus 10 may be equipped with a number ofinterchangeable tools adapted to be coupled to the drive shaft 22. Oneof these tools is a rotary cutter tool 26 including two thin rigid metalblades 27 and 28 which are rigidly secured into a hub 30 of rigidsynthetic plastic material. In looking down upon the rotary cutter tool26 of FIG. 1 in plan view, the user would see a tool which appears asshown in FIG. 2, except that the tool shown in FIG. 2 embodies theinvention as will be explained further below. Looking again at FIG. 1,the blades 27 and 28 extend out from opposite sides of the hub and havetheir root portions molded into the hub 30, so that the blades and huboperate as an integral tool. Both blades 27 and 28 are parallel to thebottom 14 of the bowl and are suitably sharpened along their leadingedges. The blade 27 is positioned at the bottom portion of the hub 30,while the other blade 28, which is on the diametrically opposite side ofthe hub as seen in plan view, is mounted significantly higher up on thehub. For example, the upper one may be positioned at an elevation whichis 3/8 of an inch or more higher than the lower one.

In order to provide a driving connection between the shaft 22 and thehub 30, the shaft 22 is formed with axially extending driving couplingmeans 32, such as a flat face or faces, square or hexagonal shape,keyway or splines. The hollow hub 30 has a socket 34 for receiving theshaft 22, and this socket 34 has complementary coupling means 36, suchas axially extending flat face, square or hexagonal hollow, internallugs, keys, or splines.

The rotary cutter tool 26 is manually installed on the drive shaft 22,or is manually removed therefrom, when the drive motor is de-energizedand the shaft 22 is stationary. For convenience of the user ininstalling or removing the rotary cutter tool 26, there may be provideda knob-like handle 37 on the upper portion of the hub 30, and thecomplementary drive coupling means 32, 36 are axially extendingcomponents. That is, their interengageable driving and driven surfacesextend longitudinally with respect to the length of the shaft 22.

Therefore, the user can quickly and easily slide the hub 30 into itsoperating position upon the shaft 22 or conversely can readily removethe hub therefrom by using a straight-line motion vertically downwardlyor upwardly. In other words, it is not necessary for the user to employa screwing or unscrewing motion to instal or remove the prior art cuttertool 26. Moreover, it is not necessary for the user to consume the timeto employ any securing or locking device, such as a nut screwed onto theupper end of the shaft 22 for holding the hub 30 onto the shaft 22.

In normal operation, the hub 30 is intended to seat fully down relativeto the shaft 22 with a stop surface of the hub resting down upon acorresponding stop associated with the shaft 22. These interengagingstop means serve to position the tool 26 in its operative locationrelative to the shaft 22. For example, the top 38 of the socket 34 andthe top 40 of the shaft 22 may serve as interengaging positioning stopmeans for locating the tool 26 in its normal operation position.Alternatively, a shoulder surface 42 on the shaft 22 and a lower endsurface 44 of the drive coupling means 36 may serve as interengagingstop means for locating this cutter tool in its proper operatingposition when the hub is slid onto the shaft 22.

Instead of directly sliding the hub 30 onto the drive shaft 22, anintermediate sleeve member, as known in the prior art (not shown), maybe keyed to this shaft, and then the hub may, in turn, be engaged withaxially extending driving coupling means formed on the exterior surfaceof such an intermediate sleeve member. Such intermediate sleeve memberwhich is operatively associated with the drive shaft may also serve toprovide positioning stop means for the rotary cutter tool 26.

Accordingly, as used herein, the term "a shaft provided with axiallyextending driving coupling means" is intended to include both,--(i) thesituation where the hub directly slides down in straight-line motion(without screwing motion) onto and engages such coupling means formed onthe shaft itself, or,--(ii) the situation where there is an intermediatecoupling member or members operatively associated with the shaft and thehub slides down in straight-line motion onto such intermediate couplingmember.

In normal operation, the blade 27 is intended to be located near thevessel bottom 14 along the length of the blade with a small spacingbetween the vessel bottom 14 and this lower blade. Moreover, this blade27 may extend out with its outer end or tip 46 closely adjacent to thevessel side wall 16 for providing a very effective food processingoperation for various kinds of foods. The upper blade 28 is shown withits tip 46 also located closely adjacent to the side wall 16.

The rotary cutter tool 26 may be used for different kinds of foodprocessing, for example, for cutting or mincing meat, for cuttingvegetables of all kinds, including condiments and for working andpreparing doughs and pastes. A relatively small quantity of foodmaterial can be processed, if desired, because of the normally smallspacing between the lower horizontal blade 27 and the horizontal bottom14. The tool 26 can also be used for preparing a mayonnaise, or anyother similar emulsion, because the lower blade 27 is closely spaced tothe bottom 14 along its length, for example, with a spacing of the orderof 5/32nds of an inch (4 millimeters) of less, thereby providing ahighly effective shearing, emulsifying action when the cutter tool 26 isin its normal operating position. Moreover, when shelled peanuts, orshelled cashew nuts, or other shelled nuts, are placed into the workingbowl 12, the rotary cutter tool 26 can process these nuts into peanutbutter or cashew butter or other nut butter.

However, in making such nut butter, using the prior art apparatus, asshown in FIG. 1, it has been my observation that the mass of partiallychopped or pulverized nuts 50 may tend to collect in the bottom of thebowl and act like a fluidized bed of particulate matter through whichthe rapidly moving lower blade 27 is slicing as it revolves at, forexample, 1,000 R.P.M. This blade has a radius to its tip 46 usuallygreater than 3 inches. Therefore, as it revolves in a circle of greaterthan onehalf a foot in diameter, at 1,000 R.P.M., it is travelling witha tip speed of at least 1,570 feet per minute, which amounts toapproximately 18 miles per hour. This relatively great velocity of thetip 46 of the blade 27 agitates the mass 50 of the partially chopped orpulverized nuts in a manner which I theorize to be somewhat analogous toa fluidized bed of material.

The undesired result is that the lower blade 27 sometimes tends to rideup or climb while moving like a hydrofoil rapidly as it slices throughthe food mass 50. The clearance between the lower revolving blade 27 andthe bowl bottom 14 progressively increases until this blade 27 isskimming or skipping along over the upper surface 52 of the foodmaterial 50. This is a dynamically stable state, as shown in FIG. 1,wherein the lower blade 27 is seen skimming at high velocity over thesurface 52 leaving substantially undisturbed the bed of chopped orpulverized nuts upon which it is moving in hydroplane fashion. The hub30 is correspondingly lifted relative to the upper end of the shaft 22,as seen in FIG. 1.

In thin horizontal metal blades 27 and 28, as shown moving rapidly, Itheorize that there is a chance for the blades, particularly the lowerone, to flex or flutter slightly as they revolve at high speed, therebyallowing food particles to get under the lower blade to accumulate therein the bed 50.

Once the cutter tool 26 has ridden up into this dynamically stablelifted position, shown in FIG. 1, it will continue in that elevatedlocation until the machine is shut off and the food material is manuallypushed aside, so that the cutter 26 can resume its normal down positionfully seated relative to the shaft 22.

This failure of the prior art apparatus 10 to complete the processing ofshelled nuts into nut butter could unexpectedly occur any time. Myexperimental trials have shown that these unexpected conditions of theblade lift and climbing action up onto the top surface 52 of the foodmass 50 are more likely to occur when there is only a modest quantity ofnuts in the bowl bottom.

The leading edges of both blades 27A and 28A are suitably sharpened bygrinding away their upper surfaces for a distance back away from theleading edge, as shown by the demarcation line at 62. The resultantsharpened leading edges 64 are thus located at the front of the lowersurface of the respective blades. These sharpened leading edges 64 maybe scalloped or serrated, or both, for enhancing the cutting or slicingaction. The sharpened leading edge 64 of each blade is angled or sweptrearwardly in the radial direction relative to the direction of rotation65. As shown in FIG. 2, sharp leading edge 64 sweeps rearwardly in acontinuous curve. This semi-crescent shape for each swept-back bladeworks to advantage in processing various foods, such as for slicing andmincing meats and for making nut butter. Such sharpened, curved,swept-back, semi-crescent-shaped blades, as seen in plan view in FIG. 2,but without the improvement claimed herein, have been provided in theprior art tool 26 of FIG. 1.

In order to overcome the unexpected dynamic lifting and hydroplaneaction, as seen in FIG. 1, of the rotary cutter tool of the prior art,an improvement is incorporated into the rotary cutter tool 26A, as seenin FIGS. 2 and 3. A downward inclination in the forward direction ofrotation 65 is provided at least in the outer portion 60 of the lowerblade 27A, particularly near its outer tip 46.

This downward inclination of the lower blade portion 60 near the tip 46may be accomplished, as shown in FIG. 3, by mounting the whole blade 27Aon the hub 30A at a negative angle of attach (-A) relative to thedirection of rotation 65. The negative angle -A is in the range fromapproximately 2° to 10° in the tip region 60 and preferably is in therange from approximately 2° to 6°. Thus, as shown in FIG. 3, as thelower blade 27A slices at high velocity through a mass of pulverulentfood material, there is a continuous impact 66 of the food materialagainst the downwardly inclined upper surface 60 near the tip region ofthe blade 27A.

This continuous impact 66 of food material is occurring at relativelyhigh velocity against the forwardly downwardly inclined blade surface60. Thereby, it develops a significant vertically downward component ofthrust 68 or "negative lift" tending to push the hub 30A down forholding it seated down in its proper operating position relative to thedrive shaft 22. If there is a sufficient depth of material in theworking bowl 12, then the downwardly inclined upper surface 60 of theupper blade 28A also develops a downward thrust or a "negative lift."However, it is the lower blade 27A which is the more important one inthis regard. Regardless of whether or not only a moderate amount ofshelled nuts may be located in the working bowl, nevertheless, thislower blade 27A will be slicing through the mass of food material andwill, therefore, develop the desired downward thrust 68.

Accordingly, the improved rotary cutter tool 26A is prevented by thedynamic operation of the rapidly revolving lower blade 27A from climbingupwardly relative to the drive shaft 22. It is my theory that thedynamic forces involved tend to be a function of the square of therelative velocity between the blade and the food particles through whichit is slicing and against which it is impacting. Force equals mass timesacceleration:

    F=ma                                                       (1)

The aggregate mass of food material "m" involved in the impact againstthe blade per unit time is a function of the volume being swept by theblade per unit time, which, in turn, is a function of relative bladevelocity (v) through the food particles:

    m=kv                                                       (2)

where "k" is a constant of proportionality.

The relative magnitude of acceleration "a" occurring at any given radialdistance from the axis of rotation is also a function of the relativeblade velocity (v) through the food particles occurring at that radialdistance.

    a=k'v                                                      (3)

where "k'" is another constant of proportionality. Substituting for "m"and "a" in equation (1) produces the result:

    F=kk'v.sup.2 =Kv.sup.2                                     (4)

where "K" is a composite function of proportionality. Thus, it is seenthat the dynamic forces 66, 68 occurring on the inclined blade surface60 near the tip region are dominant in my view, as compared with thosedynamic forces occurring on the inner region 70 of the upper surface 60near the hub 30A.

The reason that the outer portion of the blade is more important indeveloping the downward thrust is because this thrust is a function ofthe square of the relative velocity, as shown by equation (4) above, andthe tip speed of the revolving blade is much greater than in the innerregion 70 near the hub.

In the alternative embodiment 26B, as shown in FIGS. 4 and 5, the blades27B and 28B are mounted in the hub 30 with their inner portions 70substantially horizontal. In other words, these blades 27A and 28B maybe mounted in the hub 30 in the same manner as in a prior art rotarycutting tool 26 (FIG. 1). However, as shown by the shaded area 72 inFIG. 4, the outer tip portion of at least the lower blade 27B or, ifdesired, of each blade is bent upwardly along an inflection bend 74.Thus, the upper surface 60 near the respective tips 46 is inclineddownwardly relative to the direction of rotation 65. The downwardinclination is shown as the angle -A, which is in the range discussedabove. Once again, as indicated by the long arrow 66 in FIG. 5, therelatively great velocity of impact of the downwardly inclined tipportion 60 against the food material produces a downward component ofthrust or negative lift 68 serving to hold the tool 26B firmly seateddown in its normal operation position relative to the drive shaft 22.

Regardless of whether the theories of operation are correct as expressedherein, the improvement as described and claimed herein does produceadvantageous operating results in preventing the easily installedrapidly rotating tool from climbing or riding upwardly relative to thedrive shaft, regardless of the quantity or type of food material beingprocessed.

The embodiment 26B of FIGS. 4 and 5 is presently preferred because themajor portion of the cutting edge 64 of the lower blade 27B is closelyspaced to the horizontal bottom 14 of the working bowl, preferably beingspaced no more than 0.16 of an inch therefrom. For example, as shown inFIG. 4, the radius "R" to the tip 46 of the sharpened cutting edge 64 ofthe lower blade is approximately 3 inches, while the lesser radius "r"to the point 75 where the inflection bend 74 meets this cutting edge 64is approximately 2.8 inches. Thus, in this embodiment, less than 10% ofthe radial distance R to the tip 46 of the cutting edge 64 is bent up toproduce the negative angle of attack -A. The point 76 from which theradii "R" and "r" extend is the axis of rotation.

I claim:
 1. In rotary food processing apparatus having an uprightworking bowl with a vertical motor-driven shaft extending up into thebowl with its axis of rotation extending along the central axis of thebowl and in which a rotatable tool has a hub removably engaging downupon said drive shaft by a straight-line manual manipulation in drivingrelationship with the shaft provided with axially extending drivingcoupling means and such tool has a plurality of thin rigid cutter bladessecured to said hub and extending outwardly therefrom, a lower one ofsaid blades normally being positioned near the bottom of said vesselalong the length of said blade with a small spacing between the bottomof said vessel and said lower blade, and said lower blade extending outto a diameter close to the full diameter of said bottom for permittingthe operation of the apparatus with very small amounts of food, and asecond one of said blades being positioned at a higher elevation on saidhub, said lower blade having a swept back shape with its outer endtrailing behind its inner portion, the improvement comprising:means forpreventing said lower blade from dynamically climbing upwardly throughpulverulent food material being processed for preventing said hub frombeing lifted upwardly relative to said drive shaft, said preventingmeans including a downward inclination in the forward direction ofrotation of the outer portion of said lower blade for developing adownward thrust on said lower blade as the outer portion of said lowerblade revolves and moves at relatively high velocity through the foodmaterial in said working bowl, a major inner portion of the radialextent of the lower blade being substantially parallel with the bottomof said vessel, and said outer portion thereof near the tip being bentinto said downward inclination in the forward direction.
 2. In rotaryfood processing apparatus the improvement as claimed in claim 1, inwhich:said outer portion of the lower blade is bent into a negativeangle of attack in the range from approximately 2° to 10°.
 3. In arotary food processing apparatus having an upright working bowl with avertical motor-driven shaft extending up into the bowl with its axis ofrotation extending along the central axis of the bowl and in which arotatable tool has a hub removably engaging down upon said drive shaftby a straight-line manual manipulation in driving relationship with theshaft provided with axially extending driving coupling means and suchtool has a plurality of thin rigid cutter blades secured to said hub andextending outwardly therefrom, a lower one of said blades normally beingpositioned near the bottom of said vessel along the length of said bladewith a small spacing between the bottom of said vessel and said lowerblade, and said lower blade extending out to a diameter close to thefull diameter of said bottom for permitting the operation of theapparatus with very small amounts of food, and a second one of saidblades being positioned at a higher elevation on said hub, said lowerblade having a swept back shape with its outer end trailing behind itsinner portion, the improvement comprising:means for preventing saidlower blade from dynamically climbing upwardly through pulverulent foodmaterial being processed for preventing said hub from being liftedupwardly relative to said drive shaft, said means including a downwardinclination in the forward direction of rotation of the outer portion ofsaid lower blade for developing a downward thrust on said lower blade asthe outer portion of said lower blade revolves and moves at relativelyhigh velocity through the food material in said working bowl, said lowerblade having a sharp leading edge which sweeps rearwardly toward itsouter tip, said outer tip being bent upwardly into a negative angle ofattack, relative to the inner portion of the blade, and the innerportion of said sharp leading edge being positioned close to the bottomof said vessel.
 4. In rotary food processing apparatus as claimed inclaim 3, the improvement in which:less than 10% of the radial distance Rto the outer tip of the sharpened edge is bent up to provide saidnegative angle of attack.
 5. For use in rotary food processing apparatushaving an upright working bowl with a vertical motor-driven shaftextending up into the bowl with its axis of rotation extending along thecentral axis of the bowl and in which a rotatable cutter tool has aneasily installed hub removably engaging down by a straight-line manualmanipulation in driving relationship with the shaft provided withaxially extending driving coupling means and such tool has a pluralityof thin rigid cutter blades secured to said hub and extending therefrom,a lower one of said blades normally being positioned near the bottom ofsaid vessel, and said lower blade extending out to an outer tippositioned close to the side wall of said vessel and a second one ofsaid blades being positioned at a higher elevation on said hub, animproved rotary cutter tool with such easily installed hub in which:theinner portion of said lower blade near said hub is approximatelyhorizontal and the outer portion thereof near said tip is bent upwardlyrelative to the inner portion along an inflection bend forming adownward inclination in the forward direction of rotation in the outerportion thereof near said tip for providing a negative angle of attackfor developing a downward thrust on said outer portion of the lowerblade as said outer portion revolves at relatively high velocity throughfood material in said working bowl near said side wall, whereby saidrotary cutter tool is prevented from dynamically climbing upwardlythrough food material being processed to prevent the easily installedhub of said tool from being lifted upwardly relative to the drive shaft.6. For use in rotary food processing apparatus, an improved rotarycutter tool as claimed in claim 5, in which:said lower blade has asharpened leading edge with a swept back shape positioning the outer tipof said sharpened edge in trailing relationship behind the inner extentof said sharpened edge, and the inflection bend meets said sharpenededge at a point which is at least 90% of the radial distance from theaxis of rotation to said outer tip.
 7. For use in rotary food processingapparatus, an improved rotary cutter tool as claimed in claim 6, inwhich:the outer portion of said lower blade is bent up along saidinflection bend to a negative angle of attack in the range of 2° to 10°relative to the inner portion of said blade.
 8. For use in rotary foodprocessing apparatus, an improved rotary cutter as claimed in claim 6,in which:the inner extent of said sharpened leading edge of said lowerblade between the hub and said point where said inflection bend meetssaid sharpened edge is normally positioned less than 0.16 of an inchfrom the bottom of said vessel.
 9. In rotary food processing apparatushaving an upright working bowl with a vertical motor-driven shaftextending up into the bowl with its axis of rotation extending along thecentral axis of the bowl and in which a rotatable food processor toolhas an easily installed hub removably engaging down by a straight-linemanual manipulation in driving relationship with the shaft which isprovided with straight axially extending driving coupling means and suchtool has a plurality of rigid blades secured to said hub and extendingtherefrom, a lower one of said blades normally being positioned near thebottom of said vessel and extending out to an outer tip, and a secondone of said blades being positioned at a higher elevation on said hub,animproved rotary food processor tool which is at all times freelyremovable from said drive shaft by lifting said hub vertically straightupwardly along said straight axially extending driving coupling means,said improved tool having means for preventing the freely removable hubof said rotary tool from inadvertently sliding upwardly along saidstraight axially extending driving coupling means of the drive shaftduring food processing operation by preventing said lower blade fromdynamically climbing upwardly through food material being processed,said preventing means including a major inner portion of the radialextent of the lower surface of the lower blade being substantiallyparallel with the bottom of said vessel, and an outer portion of saidlower blade being inclined downwardly in the forward direction fordeveloping a downward thrust on said outer portion of the lower blade assaid outer portion revolves at relatively high velocity through foodmaterial in said working bowl.